In response to developments and innovations in many technological fields such as computing, consumer electronics, medical devices and robotics, etc., demand has increased for miniature motors that can power small mechanical and/or electromechanical devices. Examples include computer cooling fans and disc drives, medical micro-pumps, miniature laboratories, remote control vehicles, and mobile sensing devices, etc. In some applications it is also desirable that the motor have a substantially-flat shape factor to better fit within or conform to restricted space requirements.
In the prior art, brushless direct current (DC) motors have often been used where there are space or shape limitations, as these motors can be constructed in several different physical configurations that are readily adaptable for small sizing. In a configuration known as the ‘inrunner’ DC motor, permanent magnets are mounted on a spinning rotor surrounded by stationary stator windings. Another common variation is the ‘outrunner’ DC motor, in which the rotor's permanent magnets are mounted on an overhanging disc which surrounds the interior stator windings. Popular applications for disc-shaped outrunner motors include the cooling fans and disc drives found in personal computers.
The shape factors of both the inrunner and outrunner designs dictates that their drive shaft extend out-of-the-plane to the motor disc and perpendicular to the stator coils. In certain applications, however, it may be desirable to have a miniature and substantially-flat powering device having a drive shaft which lies parallel with, and not perpendicular, to the plane of the stator coils. It may also be desirable to have a powering device that can readily be scaled to meet the various power requirements of the driven devices.